1. Field of the Invention
The present invention generally relates to devices for testing the operation of an optical fiber which may be carrying a telecommunications signal, and more particularly to such a device which is usable with differing sizes of optical fibers.
2. Description of the Prior Art
Optical fiber identifiers are known in the art, and are generally used to determine whether an optical fiber is carrying an optical signal, particularly a test signal. These devices are commonly used in the testing of fibers carrying telecommunications signals, including voice and data. Fiber identifiers operate by extracting a minute portion of the light signal at a small bend in the fiber. See U.S. Pat. No. 5,138,690 for a discussion of additional operating details as well as a list of prior art patents.
There are still many disadvantages with prior art fiber identifiers. Several of these relate to the use of an identifier for testing different sizes of fibers. Most identifiers are made to handle only a single type or size of fiber, particularly 250 .mu.m. Other units which claim to handle all fibers (e.g., Noyes' OFI-200, or Wilcom's F6222) provide only clumsy solutions, and present additional technical problems.
For example, some devices designed for different types of fibers use a single piston to force the fiber against a detector head and consequently fail to meet industry (Bellcore) bend loss requirements for all of the different sizes. Excessive bend loss may cause line interruption as explained in the '690 patent. In those instruments where two or more pistons are used, the device must be partially disassembled to gain access to and replace the piston. Such devices still fail to maintain repeatable bend loss specifications due to lack of constant pressure on the fiber. In particular, user-dependent pressure (i.e., manual gripping) not only fails to sometimes further causes excessive bend loss.
Another problem associated with existing multiple size fiber identifiers is the fiber handling mechanism. The performance of these devices heavily depends on how the user installs the fiber in the device head. The user must also learn different techniques for installing different fibers, e.g., at different positions in the clip-on head mechanism.
Performance also depends greatly on ambient light leakage into the detector head of the device. Too much ambient light leakage not only limits sensitivity but further may cause false identification of a light signal on the fiber. The craftsperson might unwittingly cause damage to the fiber due to this false identification. In some devices ambient light shielding may be sufficient in darker environments, but the devices become useless in excessively bright conditions (e.g., sunlight or intense room light), limiting the real-life uses of the device. It would, therefore, be desirable to devise a fiber identifier which is easily used with fibers of differing sizes and which guarantees repeatable bend loss. It would be further advantageous if the unit was highly sensitive to low power signals in any ambient lighting conditions.